The Universal Mobile Telecommunication System (UMTS), also referred to as the third generation (3G) system or the wideband code division multiplexing access (WCDMA) system, is designed to succeed GSM. UMTS Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS system.
High-Speed Downlink Packet Access (HSPDA) is an evolution of UTRAN bringing further enhancements to the provisioning of packet-data services both in terms of system and end-user performance. The downlink packet-data enhancements of HSDPA are complemented with Enhanced Uplink (EUL), also known as High-Speed Uplink Packet Access (HSUPA). EUL provides improvements in the uplink capabilities and performance in terms of higher data rates, reduced latency, and improved system capacity, and is therefore a natural complement to HSDPA. HSDPA and EUL are often jointly referred to as High-Speed Packet Access (HSPA). In the HSPA architecture, a user equipment (UE) 150 is wirelessly connected to a radio base station, i.e. a NodeB 130, as illustrated in FIG. 1.
The operation of WCDMA/HSPA on multiple 5 MHz frequency blocks—so called carriers—used simultaneously for one given UE, is one further step of evolving WCDMA and HSPA. This mode of operation is often referred to as multi-carrier HSPA.
A multi-carrier connection with frequency division duplex (FDD) can be described as a set of downlink carriers linked to a set of uplink carriers for a given UE. The downlink carriers can be adjacent or non-adjacent in the frequency domain, and the same holds for the uplink carriers. More generally speaking, the carriers do not need to be in the same frequency band, and time division duplex (TDD) bands could also be used as part of the multi-carrier operation. The number of downlink carriers may also be different from the number of uplink carriers in a multi-carrier connection for a given UE. If there is one uplink carrier, the number of downlink carriers can for example be two or more. The opposite with more uplink carriers than downlink carriers is also possible. Hereinafter, the “multi-carrier symmetry” of a connection refers to the number of uplink and downlink carriers in the multi-carrier connection for a given UE.
Conventionally, one anchor carrier can be defined in uplink and one in downlink, in a multi-carrier connection. The remaining carriers (uplink and downlink) can then be referred to as non-anchor (NA) carriers. For example, most of the control signaling can be carried on the anchor carrier, while the non-anchor carriers carry only the data channels and necessary control signaling channels that cannot be carried on the anchor carrier.
In prior art, WCDMA/HSPA systems make use of a mechanism to control the transmit power of the fractional downlink physical control channel (F-DPCH), which is the downlink channel that carries transmit power control commands from the NodeB to the UE used by the UE to adjust the transmit power of the uplink carrier. With this mechanism the transmit power control (TPC) commands are defined by the UE, based on measurements of the signals received from the NodeB. The TPC command can indicate either “up” corresponding to a power increase of e.g. 1 dB, or “down” corresponding to a power decrease. The TPC commands are transmitted on an uplink control channel, in order for the NodeB to adjust the downlink transmit power of the F-DPCH.
In a conventional multi-carrier HSPA system, there can be different multi-carrier symmetries with multiple downlink carriers and/or multiple uplink carriers for a given UE, as described above. The different carriers may use adjacent or non-adjacent frequency bands. A multi-carrier system also operates in soft handover scenarios. In all multi-carrier systems, there is a need to control the transmission power of the downlink carriers' F-DPCH. Downlink power control mechanisms has to be defined, going beyond the mechanisms used in single-carrier systems with only one uplink and one downlink carrier, e.g. because channel conditions may differ between different (potentially non-adjacent) downlink carriers. Thus, there is a need to provide an efficient and reliable control of the downlink transmit power of F-DPCH in a multi-carrier HSPA system, regardless of e.g. the multi-carrier symmetry and the used frequency bands for the different carriers.